A rookie Connecticut cop claimed he needed time off from work for US Army Reserve training – when he was really off in Hawaii on vacation with his girlfriend, authorities said.

When Stamford police officer Donald Chen was caught in the lie, he resigned — and now faces criminal charges of felony larceny and fraud, according to the Stamford Advocate.

“I’m extremely disappointed with what happened,” Stamford police chief Jon Fontneau said. “What we found to be was a case of fraud committed not only to the city of Stamford and its taxpayers but the US Government.”

Chen allegedly told supervisors he was going to be away for training from Dec. 1 to 15 and his department – which allows for 30 days of paid leave for deployment — granted that time off.

The story fell apart when — eight days into the faux military leave — Army officials called Stamford PD looking for Chen and alarmed cops launched a missing persons probe, officials said.

Chen eventually reached out to Stamford PD and said he had to rush to Taiwan where his dad had a heart attack and was undergoing surgery, said internal affairs commander Lt. Sean Cooney.

Cops double-checked Chen’s story and found that mom and dad were alive and well in Queens, allegedly forcing the embattled officer to admit he was in Hawaii with his gal pal.

Chen, who had been on the force since April 2014, resigned on Dec. 14.

Had he not quit, “he would have been fired,” according to Fontneau.

Chen’s lawyer said his client has served in the Army Reserves for eight years, with time in both Iraq and Afghanistan.

Chen “has the support of a great group of friends and his family at this time,” said defense lawyer John Gulash said